The predominant approach today to introduce factory automated technology into manufacturing is to selectively apply automation and create islands of automation. The phrase "islands of automation" has been used to describe the transition from conventional or mechanical manufacturing to the automated factory.
Manufacturing examples of islands of automation include robots for assembly, inspection, painting and welding. To date the major application for industrial robots has been material handling. Included here are such tasks as machine loading and unloading; palletizing/depalletizing; stacking/unstacking; and general transfer of parts and materials - for example between machines or between machines and conveyors.
An example of one such application is disclosed in the U.S. Patent to Kenmochi U.S. Pat. No. 4,519,761.
The '761 Patent discloses a combined molding and assembling apparatus wherein a pallet is conveyed by a conveyor.
The U.S. Patent to Horvah U.S. Pat. No. 4,696,351 discloses a robot having a holder for parts in an assembly area and a head carrying an assembly tool. The head is movable with respect to the part holder by guide supports and is positioned by motors. The head carries in its fixed or sliding mode a device enabling to apply the tool to a part with a predetermined force.
Robots are often an essential ingredient in the implementation of Flexible Manufacturing Systems (FMS) in the automated factory. Early examples of the use of robots for assembling small parts is disclosed in the U.S. Patents to Engelberger et al U.S. Pat. Nos. 4,163,183 and 4,275,986 wherein robots are utilized to assemble parts from pallets onto a centrally located work table. The U.S. patents to Abe et al U.S. Pat. No. 4,611,380 and Suzuki U.S. Pat. No. 4,616,411 disclose fastening apparatus including a bolt receiving and supply device for use in the automated assembly of a door to a vehicle.
The U.S. Patent to Suzuki et al U.S. Pat. No. 4,383,359 discloses a part-feeding and assembling system including multiple stage vibration and magazine feeders. A robot is utilized to change the position of the fed parts for assembly on a chassis supported on a line conveyor.
The major impediment to robotic assembly is economic justification. When the cost of robotic assembly is compared against traditional manual methods or high volume dedicated machinery, robots oftentimes lose out to the high volume, high speed application where hard automation is used. It is difficult for robots to compete in that environment.
On the other side are the low volume, high variety products that are assembled manually. Robots may lack the dexterity to perform these jobs and they may cost more than relatively low paid manual assemblers. There is a middle ground between these two extremes for flexible assembly.
Traditionally, there have been other barriers to the use of robots in mechanical assembly. They include the following: (1) the high cost of engineering a new system which may run three to five times the costs of the robot itself; (2) the amount of time it takes to engineer the system; (3) the difficulty of coordinating multiple robot arms; (4) the difficulty of integrating an assembly system; (5) the high cost of tooling software sensors, part presentation equipment and other peripherals; (6) the difficulty of finding knowledgeable personnel; (7) insufficient speed, lift capacity and positioning accuracy and repeatability on the part of the robots; and (8) a lack of supporting technology in such areas as high level programming languages, end of arm tooling and sensors.
Assembly robots offer an array of benefits that cannot be ignored. They can produce products of high and consistent quality in part because they demand top quality components. Their reprogrammability allows them to adapt easily to design changes and to different product styles. Work in process inventories and scrap can be reduced.
The U.S. Patent to Mayamamoto U.S. Pat. No. 4,594,764 discloses an automated apparatus and method for assembling parts in a structure member such as an instrument panel of an automobile. A conveyor conveys the jig which supports the panel to and from assembly stations. Robots mount the parts on the instrument panel at the assembly stations. Robots are provided with arm-mounted, nut-driving mechanisms supplied from vibratory parts bowls. Vacuum-type grippers and electromagnetic grippers are advantageous because they permit part acquisition from above rather than from the side. This avoids the clearance and spacing consideration that are often involved when using mechanical grippers.
However, the use of vacuum and electromagnetic grippers is not without its problems. Cycle time is not just a function of robot speed and acceleration/decelerating characteristics. Cycle time is also dependent on how fast the robot can move without losing control of the load. Horizontal shear forces must be considered in the application of these grippers. This often means that the robot is run at something less than its top speed.
A wide variety of tools have been used by robotic manipulators. Such tools include screw fastening units. United States Patents to Booker U.S. Pat. No. 4,561,506 and Saito U.S. Pat. No. 4,637,776 are examples of such screw-fastening units mounted on a robotic manipulator for movement therewith.
The U.S. Patent to Yasukawa U.S. Pat. No. 4,518,298 discloses a head for an industrial robot which operates at a relatively high speed and with a relatively small drive force. A motor generates rotational torque to a nut member through a rotational coupling mechanism.